1. Field of the Invention
The present invention relates to an optical writing device that includes a plurality of semiconductor lasers and is capable of adjusting amounts of the laser beams by using a photo sensing element, a controlling method thereof, and an image forming apparatus including the optical writing device.
2. Description of the Related Art
In the related art, a conventional image forming apparatus equipped with an optical writing device has a laser chip including a light emitting element and a photo sensing element (for example, a photo diode), and a semiconductor laser controller including an optical negative feed back loop for control of the laser chip. In order to increase printing speed and image quality of the image forming apparatus, a number of laser chips and the same number of laser controllers are provided in the image forming apparatus.
To increase the printing speed and image quality, a laser chip is proposed which includes a number of light emitting elements arranged in a matrix manner, forming a light emitting element array.
When using the light emitting element array including a number of light emitting elements arranged in a matrix manner in a laser chip, because there is only one photo sensing element commonly used by the light emitting elements, it is difficult to perform an APC (Auto Power Control) operation for the light emitting elements at the same time. As a result, it is difficult to apply the APC pull-in technique of the related art directly to the light emitting element array configuration used in a multi-beam writing device.
In the image forming apparatus of the related art, for example, as disclosed in Japanese Laid Open Patent Application, No. 10-166649, which discloses a method of APC pull-in process suitable for a multi-beam writing device, any one of the light emitting elements can be used to generate laser beams to successively generate synchronization signals. In synchronization with the synchronization signals, the powers (or, the amount of light emitted from a light emitting element) of other light emitting elements are adjusted to a desired value.
However, in the image forming apparatus disclosed in Japanese Laid Open Patent Application, No. 10-166649, when a light emitting element is turned on to generate a synchronization signal, adjustments of other light emitting elements have to be interrupted, and the adjustments have to be monitored constantly.